Method and apparatus to optically detect defects in transparent solids

ABSTRACT

A method and apparatus to measure specular reflection intensity, specular reflection angle, near specular scattered radiation, and large angle scattered radiation and determine the location and type of defect present in a first and a second transparent solid that have abutting surfaces. The types of defects include a top surface particle, an interface particle, a bottom surface particle, an interface bubble, a top surface pit, and a stain. The four measurements are conducted at multiple locations along the surface of the transparent solid and the measured information is stored in a memory device. The difference between an event peak and a local average of measurements for each type of measurement is used to detect changes in the measurements. Information stored in the memory device is processed to generate a work piece defect mapping indicating the type of defect and the defect location of each defect found.

TECHNICAL FIELD

The described embodiments relate generally to detecting defects and moreparticularly to detecting defects in a two transparent solids withabutting surfaces.

BACKGROUND INFORMATION

Transparent solids are used to form various products such as display andtouch screen devices. The inspection of transparent solids iscomplicated by the difficulty of separating the scattered lightreflected from the top and bottom surfaces of a transparent solid. Thisdifficulty is further complicated when a first transparent solid islocated on a second transparent solid.

SUMMARY

A surface optical inspector directs a source beam onto a surface of atransparent solid that is placed on top of a second and in responsemeasures various types of radiation from the work piece. The types ofradiation include specular reflection, specular reflection angle, nearspecular scattered radiation, and large angle scattered radiation. Themeasured information is processed to determine the total reflectivity ofthe work piece, the surface slope of the work piece, large anglescattered radiation intensity from the work piece, and near specularscattered radiation intensity from the work piece. These measurementsare in turn utilized to determine the type of defect present at the scanlocation and on which surface of which transparent solid the defect islocated.

In a first novel aspect, a scanning beam is directed to a first locationon a first surface of a first transparent solid and a second surface ofthe first transparent solid abuts a first surface of a secondtransparent solid. At the first location the following measurements aremade: (i) specular reflection intensity, (ii) Near Specular ScatteredRadiation (NSSR) intensity, (iii) Large Angle Scattered Radiation (LASR)intensity, and (iv) Specular Reflection Angle. Measurements (i) through(iv) result from irradiation by the scanning beam. Then coordinatevalues of the first location, and measurements (i) through (iv) arestored in a memory.

In one example, the measurements are measured across the entire surfaceof the first transparent solid. At each location along the surface ofthe transparent solid a determination as to what type of defect ispresent at the location. The types of defects are selected from a groupcomprising: (1) a top surface particle, (2) an interface particle, (3) abottom surface particle, (4) an interface bubble, (5) a top surface pit,and (6) a stain.

In a second novel aspect, a type of defect at the first location is aninterface particle when: (i) the LASR measured at the first locationless than a first percentage (fifty-percent) of the NSSR measured at thefirst location; (ii) the specular reflection intensity measured at thefirst location is within a second percentage (a tenth of a percent) of alocal average of specular reflection intensity or greater; and (iii) thespecular reflection angle transitions from a positive angle to anegative angle at the first location. The local averages are a functionof multiple measurements measured at a multiple locations that arewithin a first distance of the first location.

In a third novel aspect, the type of defect at the first location is aninterface bubble when: (i) the LASR measured at the first location isless than a first percentage (fifty percent) of the NSSR measured at thefirst location; (ii) the specular reflection intensity measured at thefirst location is more than a second percentage (one half of onepercent) greater than a local average of specular reflection intensityor greater; and (iii) the specular reflection angle oscillates betweenpositive angles and negative angles near the first location. The localaverages are a function of multiple measurements measured at a multiplelocations that are within a first distance of the first location.

In a fourth novel aspect, type of defect at the first location is a topsurface particle when: (i) the LASR measured at the first location ismore than a first percentage (twice as large) of the LASR measured atthe second location, and the LASR measured at a first location is morethan a second percentage (twice as large) of the NSSR measured at thefirst location, wherein the first location is within a first distance ofthe second location; (iii) the specular reflection intensity measured atthe first location is within a third percentage (ten percent) of a localaverage of specular reflection intensity, or more; (iv) the specularreflection angle is within a fourth percentage (one percent) of a localaverage of specular reflection angles. The local averages are a functionof multiple measurements measured at a multiple locations that arewithin a first distance of the first location.

In a fifth novel aspect, the type of defect at the first location isbottom surface particle when: (i) the LASR measured at the firstlocation is at least a first percentage (twice as large) of the NSSRmeasured at the first location; (ii) the specular reflection intensitymeasured at the first location is within a second percentage (onepercent) of the local average of specular reflection intensity; and(iii) the specular reflection angle is within a third percentage (onepercent) of a local average of specular reflection angles. The localaverages are a function of multiple measurements measured at a multiplelocations that are within a first distance of the first location.

In a sixth novel aspect, the type of defect at the first location is topsurface pit when: (i) the LASR measured at the first location is withina first percentage (one percent) of a local average of LASR, and lessthan a second percentage (fifty percent) of the NSSR measured at thefirst location; (ii) the specular reflection intensity measured at thefirst location is at least a third percentage (tenth of a percent) lessthan a local average of specular reflection intensity; and (iii) thespecular reflection angle transitions from a negative angle to apositive angle at the first location. The local averages are a functionof multiple measurements measured at a multiple locations that arewithin a first distance of the first location.

In a seventh novel aspect, type of defect at the first location is astain when: (i) the LASR measured at the first location is at least afirst percentage (tenth of a percent) greater than a local average ofLASR intensities; (ii) the NSSR measured at the first location is lessthan the LASR intensity measured at the first location; (iii) thespecular reflection intensity measured at the first location is lessthan a local average of specular reflection intensities; and (iv) thespecular reflection angle is within a second percentage (one percent) ofa local average of specular reflection angles. The local averages are afunction of multiple measurements measured at a multiple locations thatare within a first distance of the first location.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a cross-sectional diagram illustrating the interface of twotransparent solids.

FIG. 2 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y1).

FIG. 3 is a specular reflection mapping illustrating the specularreflection resulting from the irradiation at position (X1, Y1).

FIG. 4 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y4).

FIG. 5 is a specular reflection mapping illustrating the specularreflection resulting from the irradiation at position (X1, Y4).

FIG. 6 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y2) causing top surface forward scattered radiation caused by a topsurface particle.

FIG. 7 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y3) causing top surface back scattered radiation caused by a topsurface particle.

FIG. 8 is a large angle scattered radiation mapping illustrating thelarge angle scattered radiation resulting from the irradiation atposition (X1, Y2) and position (X1, Y3) illustrated in FIGS. 6 and 7.

FIG. 9 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y5) causing bottom surface back scattered radiation caused by abottom surface particle.

FIG. 10 is a large angle scattered radiation mapping illustrating thelarge angle scattered radiation resulting from the irradiation atposition (X1, Y5) illustrated in FIG. 9.

FIG. 11 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y6) causing near specular scattered radiation caused by aninterface particle.

FIG. 12 is a diagram of a near specular scattered radiation mappingillustrating the near specular scattered radiation resulting from theirradiation at position (X1, Y6) illustrated in FIG. 11.

FIG. 13 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y0) causing near specular scattered radiation caused by a topsurface pit.

FIG. 14 is a diagram of a near specular scattered radiation mappingillustrating the near specular scattered radiation resulting from theirradiation at position (X1, Y0) illustrated in FIG. 13.

FIG. 15 is a top view diagram of a first optical inspector.

FIG. 16 is a top view diagram of a second optical inspector.

FIG. 17 is a diagram illustrating a perspective view of a large anglescattered radiation optical inspector.

FIG. 18 is a diagram of a specular reflection intensity mappingillustrating the specular reflection resulting from the irradiation atposition (X1, Y1) and (X1, Y4) illustrated in FIGS. 2 and 4.

FIG. 19 is a diagram of a scattered radiation intensity mappingillustrating the scattered radiation resulting from the irradiation atposition (X1, Y2), (X1, Y3), and (X1, Y5) illustrated in FIGS. 6, 7, and9.

FIG. 20 is a diagram of defect detection and classification logic table.

FIG. 21 is a diagram illustrating definitions of event intensities.

FIG. 22 illustrates a result work piece defect mapping that is generatedby applying the logic described in the table of FIG. 20 to measurementsmeasured across the surface of the work piece.

FIG. 23 is a flowchart 200 illustrating the steps included in the defectdetection process.

FIG. 24 is a diagram illustrating the position and functionality of aseparation mirror.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings. In the description and claims below, relationalterms such as “top”, “down”, “upper”, “lower”, “top”, “bottom”, “left”and “right” may be used to describe relative orientations betweendifferent parts of a structure being described, and it is to beunderstood that the overall structure being described can actually beoriented in any way in three-dimensional space.

FIG. 1 is a cross-sectional diagram illustrating the interface of twotransparent solids. During the fabrication of transparent solids (alsoreferred to transparent work pieces, transparent layers, transparentwafers, and transparent discs) unwanted defects can be produced. Theseunwanted defects include a top surface particle 3, an interface particle4, a bottom surface particle 5, an air gap, (also referred to as a“bubble”) 6, and a top surface pit 22 illustrated in FIG. 13. Thesedefects may occur in various locations on the transparent solids. Thesedefects result in undesirable results such as reduced operating life ofthe resulting display device, non-functionality of the resulting displaydevice, and degraded performance (light efficiency) of the resultingdisplay device. It is valuable to a display manufacturer to detect thesedefects before additional resources are spent developing a product thatwill not function properly due to wafer level defects. For example, a“bubble” at the interface may produce unwanted topography on the topsurface of the transparent solid and this may interfere with the abilityto focus a lithography pattern on the surface. Particles on the topsurface may cause electrical shorts to appear when metal lines aredeposited on this surface.

It is noted herein, the example of two layers of glass is used forexemplary use only. This disclosure is not limited to the detection ofdefects in two layers of glass. Rather, this disclosure is applicable toall transparent layers or wafers or discs regardless of the specificmaterial constituting the layer/wafer/disc or the end device to bemanufactured with the developed layers/wafer/disc. For example, siliconis opaque in the visible range of the spectrum but transparent in theinfrared spectrum. As a result this disclosure applies to the case of awork piece consisting of glass and a platform composed of silicon whenthe illuminating wavelength is in the infrared spectrum. It would alsoencompass the reverse case of a work piece consisting of silicon and aplatform consisting of glass.

The first transparent solid 2 in FIG. 1 is a less than one millimeterthick. The second transparent solid 1 in FIG. 1 is approximately onemillimeter thick. The second transparent solid 1 acts as a platform tohold the thinner and less durable first transparent solid which isreferred to as a work piece.

FIG. 2 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam 7 directed at position locatedat (X1, Y1). The scanning beam 7 scans across the work piece 2 in adirection going in the Y-direction (in and out of the page). Significantspecular reflection 8 is reflected from the top surface of the workpiece 2. Significant specular reflection 9 is also reflected from thebottom surface of the carrier 1. Specular reflections 8 and 9 are ofsimilar intensity. There is no significant specular reflection from theinterface between the work piece 2 and the platform 1 at position (X1,Y1) because the work piece 2 and the platform 1 are in intimate contactat position (X1, Y1) and because the work piece 2 and the platform 1have a similar index of refraction.

FIG. 3 is a specular reflection mapping illustrating the specularreflection resulting from the irradiation at position (X1, Y1)illustrated in FIG. 2. The specular reflection intensity at position(X1, Y1) indicates that that the work piece 2 and the platform 1 are inintimate contact and that no particles or pits are present at location(X1, Y1).

FIG. 4 is a cross-sectional diagram illustrating the interface of twotransparent solids, work piece 2 and platform 1, with a scanning beam 7directed at position located at (X1, Y4). Significant specularreflection 11 is reflected from the top surface of the work piece 2 dueto the change of the index of refraction of air and the index ofrefraction of work piece 2. Significant specular reflection 12 isreflected from the bottom surface of the work piece 2 due to the changein the index of refection of the work piece 2 and index of refraction ofthe air trapped in air gap 6. Significant specular reflection 13 isreflected from the top surface of platform 1 due to the change in theindex of refraction of the air trapped in air gap 6 and the index ofrefraction of platform 1. Significant specular reflection 14 isreflected from the bottom surface of platform 1 due to the change in theindex of refraction of the platform to the index of refraction of air.

FIG. 5 is a specular reflection mapping illustrating the specularreflection resulting from the irradiation at position (X1, Y4). Asillustrated in FIG. 4, specular reflections 11-14 do not directlyoverlap, but rather are spread across a wide area. Accordingly,increased specular reflection intensity is observed at (X1, Y4) in theresulting specular reflection mapping shown in FIG. 5 indicating thepresence of an air gap at location (X1, Y4).

FIG. 6 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y2) causing top surface forward scattered radiation caused by a topsurface particle 3. Significant forward scattered radiation 15 isradiates from top surface particle 3 due to irradiation of the topsurface particle 3 by specular reflection 16 which reflects from thebottom surface of platform 1. Specular reflection 16 is caused by thechange of the index of refraction between the platform 1 and air.

FIG. 7 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam 7 directed at position locatedat (X1, Y3) causing top surface back scattered radiation 17 caused by atop surface particle 3. Scanning beam 7 directly irradiates the topsurface particle located at (X1, Y3) causing back scattered radiation17.

FIG. 8 is a large angle scattered radiation mapping illustrating thelarge angle scattered radiation resulting from the irradiation atposition (X1, Y2) and position (X1, Y3) illustrated in FIGS. 6 and 7.The pair of large angle scattered radiation increased intensitiesindicates that a top surface particle is present at location (X1, Y3).The back scattered radiation intensity is significantly greater than theintensity of the forward scattered radiation.

FIG. 9 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y5) causing bottom surface back scattered radiation caused by abottom surface particle. Scanning beam 7 irradiates the top surface ofthe work piece 1 and is slightly redirected due the change in the indexof refraction of air and the index of refection of the work piece 2 andcauses the bottom surface particle 5 located at (X1, Y5) to beirradiated. The irradiation of the bottom surface particle 5 causes backscattered radiation 19 to emit from the bottom surface particle 5.

FIG. 10 is a large angle scattered radiation mapping illustrating thelarge angle scattered radiation resulting from the irradiation of thebottom surface particle 5 located at position (X1, Y5) illustrated inFIG. 9. In contrast to two increased intensities in scattered radiation,presence of a single increased intensity in scattered radiationindicates the presence of a bottom surface particle at location (X1,Y5). In one example, two increases in scattered radiation must be withinone hundred microns of each other in order to be considered a pair ofincreased scattered radiation intensities (also referred to herein as a“double event”) and if the two increases in scattered radiation are notwithin one hundred microns of each other then each increase in scatteredradiation is considered a single increase in scattered radiation (alsoreferred to herein as a “single event”). In a second example, to beconsidered a “double event” both increases in scattered radiation mustbe within fifty microns of each other. As one skilled in the art willquickly ascertain, the separation limits between increased intensitiesof scattered radiation will vary depending on setup, environment, workpiece material and thickness, platform material and thickness, andparticles types to be detected.

FIG. 11 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam directed at position located at(X1, Y6) causing irradiation of small interface particle 20. Theirradiation of small interface particle 20 causes near specularscattered radiation 21 to emit from the small interface particle 20. Thenear specular scattered radiation 21 is predominately in the upwarddirection close to the specular reflection path.

FIG. 12 is a diagram of a near specular scattered radiation mappingillustrating the near specular scattered radiation 21 resulting from theirradiation at position (X1, Y6) illustrated in FIG. 11. The increase innear specular scattered radiation (also referred to herein as “NSSR”)indicates the presence of a small interface particle located at position(X1, Y6).

FIG. 13 is a cross-sectional diagram illustrating the interface of twotransparent solids with a scanning beam 7 directed at position locatedat (X1, Y0) causing near specular scattered radiation due to a topsurface pit 22. The scattering of scanning beam 7 off the top surfacepit 22 causes a near specular scattered radiation 23 to radiate from thetop surface of work piece 2. The near specular scattered radiation 23 ispredominately in the upward direction along the specular reflectionpath.

FIG. 14 is a diagram of a near specular scattered radiation mappingillustrating the near specular scattered radiation resulting from theirradiation at position (X1, Y0) illustrated in FIG. 13. An increase innear specular scattered radiation at position (X1, Y0) indicates thepresence of a top surface pit at location (X1, Y0). Given that the samephenomenon is measured for a small interface particle illustrated inFIG. 12 additional measurements are required to differentiate between anincrease in NSSR due to a small interface particle and an increase inNSSR due to a top surface pit. The details of these additionalmeasurements are shown in FIG. 20.

FIG. 15 is a top view diagram of an optical inspector. The opticalinspector includes a radiating source 30, an outgoing half waveplate 31,a time varying beam reflector (rotating polygon 32), a telecentric scanlens 33, a start scan detector 36, a first mirror 37, a second mirror38, a separation mirror 41, a first aperture 42, a first neutral densityfilter 50, a bi-cell photo detector 43, a second aperture 45, a secondneutral density 46, a detector 47, a processor 48, and a memory 49. Itis noted herein, the use of rotating polygon is exemplary. Any timevarying beam reflector, such as a resonant galvanometer, a rotatingdouble sided mirror, or acousto-optic beam deflector can be utilized aswell.

The radiating source 30 irradiates outgoing half waveplate 31 with asource beam. In one example, the radiating source 30 is a laser.Outgoing half waveplate 31 converts the linearly polarized source beamto a forty-five degree rotated linearly polarized beam. The rotatedlinearly polarized beam is directed by the rotating polygon 32 to afirst location on the telecentric scan lens 33. The angle at which thesource beam approaches the telecentric scan lens 33 depends upon theangle of rotation of the rotating polygon 32 when the source beamcontacts the rotating polygon 32. However, regardless of the angle atwhich the source beam approaches the telecentric scan lens 33, thetelecentric scan lens 33 directs the source beam to a work piece 34 atan angle that is substantially normal to the surface of the work piece34. In one example, the work piece is the transparent wafer (work piece1) shown in FIG. 1 and the telecentric scan lens 33 directs the sourcebeam to the work piece 34 at an angle of approximately three degreesfrom normal.

The source beam directed, at a substantially normal angle, to the workpiece 34 generates a reflection of the source beam. A first portion ofthe reflected source beam is specular reflection. A second portion ofthe reflected source beam is near specular scattered radiation. Specularreflection is the mirror-like reflection of light from a surface, inwhich light from a single incoming direction is reflected into a singleoutgoing direction (in adherence with the law of reflection). Nearspecular scattered radiation is light which is scattered (or deflected)by defects in a region which is just outside the profile of the specularbeam. Measuring both the specular reflection and the near specularscattered radiation allows the detection of defects which may not bevisible in the specular reflection alone.

The reflected radiation, including specular reflection 39 and the nearspecular scattered radiation 40, is reflected back to the telecentricscan lens 33. The telecentric scan lens 33 directs the specularreflection 39 and the near specular scattered radiation 40 to therotating polygon 32. The rotating polygon 32 directs the specularreflection 39 and near specular scattered radiation 40 back toward theradiating source 30. At this point, separating the source beam from thereflected light would be impractical if both the source beam and thereflected beams were traveling in the same space. To avoid thisproblematic situation, the radiating source 30 is placed at a locationat an offset from the central axis of the telecentric scan lens 33. Thisdirects the reflected radiation away from the radiating source 30without altering the source beam radiating from the radiating source 30.

Mirror 37 reflects both specular reflection 39 and near specularscattered radiation 40 to mirror 38. Mirror 38 in turn reflects bothspecular reflection 39 and near specular scattered radiation 40 toseparation mirror 41. Separation mirror 41 reflects a portion of thenear specular scattered radiation 40 toward aperture 45 while notreflecting specular reflection 39. The reflected portion of the nearspecular scattered radiation passes through aperture 45 and neutraldensity filter 46 and irradiates detector 47. Specular reflection 39passes separation mirror 41 and passes through aperture 42 and neutraldensity filter 50 and irradiates detector 43.

Separation mirror 41 is positioned so that specular reflection 39 doesnot irradiate the separation mirror 41 while the near specular scatteredradiation 40 does irradiate the separation mirror 41. Consequently, onlya portion of the near specular scattered radiation 40 is reflected bythe separation mirror 41. In a first example, the separation mirror 41is positioned above the path of specular reflection 39. In a secondexample, the separation mirror 41 is positioned below the path ofspecular reflection 39. This example is illustrated in FIG. 24 showingthe function of separation mirror 41 in greater detail.

Aperture 42 is positioned between separation mirror 41 and bi-celldetector 43. Aperture 42 serves to block any near specular scatteredradiation directed toward bi-cell detector 43 from mirror 38. In analternative example, aperture 45 is included between mirror 41 andphotomultiplier tube detector 47. Aperture 45 serves to block anynon-near specular scattered radiation directed toward photomultipliertube detector 47 from separation mirror 41.

Neutral density filter 50 is positioned between aperture 42 and bi-celldetector 43. Neutral density filter 50 reduces the intensity of thespecular reflection 39 that irradiates the bi-cell detector 43. Theability to vary the intensity of the specular reflection 39 providescontrol regarding detector sensitivity.

Neutral density filter 46 is positioned between aperture 45 andphotomultiplier tube detector 47. Neutral density filter 46 reduces theintensity of the near specular scattered radiation 40 that irradiatesthe photomultiplier tube detector 47. The ability to vary the intensityof the near specular scattered radiation 40 provides control regardingdetector sensitivity.

The bi-cell detector 43 is located such that the specular reflection 39should irradiate the bi-cell detector 43 on the center line 44 betweenthe two photodiodes included in the bi-cell detector 43. In the eventthat the surface slope (the “micro-waviness”) of the work piece is notnormal to the source beam, the resulting specular reflection 39 willdeviate from the center line 44. A deviation from the center line 44will cause a greater amount of the specular reflection 39 to irradiateone of the two photodiodes in the bi-cell detector 43. In response, thebi-cell detector 43 will output an increased difference value indicatinga change in the slope of the work piece 34 surface. A negativedifference value indicates a slope varying in a first direction. Apositive difference value indicates a slope varying in a seconddirection. The slope measured is the surface slope of the work piece 2in direction perpendicular to the optical scan line. Regardless of thedeviation of the specular reflection 39 from the center line 44, thebi-cell detector 43 will output a sum value indicating the reflectivityof the work piece 34.

In another example, a processor 48 is also included in the top surfaceoptical inspector shown in FIG. 15. The processor 48 receives theintensity output signal from the photomultiplier tube detector 47, adifference output signal from bi-cell detector 43, a sum output signalfrom bi-cell detector 43. In response, processor 48 determines whetherdefects are present at the scan location on the work piece 34.

The processor may also communicate with a motor controlling rotatingpolygon 32. The processor may increase or decrease the rate of rotationof the rotating polygon 32. For example, when switching from using ahigh-bandwidth detector to a low-bandwidth detector, it may be requiredthat the rate of rotation of the rotating polygon 32 be decreased.Alternatively, when switching from using a low-bandwidth detector to ahigh-bandwidth detector, it may be necessary to increase the rate ofrotation of the rotating polygon 32.

In another example, memory 49 is included in the top surface opticalinspector shown in FIG. 15. Memory 49 stores information output byprocessor 48. (i.e. defect information, or defect indicatorinformation). Memory 49 also stores location information indicating thelocation on the work piece which was scanned to measure the defectinformation or defect indicator information. Defect information is astatus as to whether the scanned location on the work piece contains adefect or not. Defect indicator information includes variousmeasurements from the scanned location on the work piece (i.e. surfaceslope, total reflectivity, intensity of scattered radiation, intensityof near specular scattered radiation).

The amount of near specular scattered light which is collected islimited by the size of the polygon mirror facets. The near specularscattered radiation reflects off the separation mirror 41 and isincident on the photomultiplier tube (PMT) detector. The PMT measuresthe intensity of the near specular scattered light. Localized defectswill appear as variations (increases or decreases) in the near specularscattered light signal.

In one example, the scan of the work piece is done with the polygonrotating at a high speed and the data sampling of the bi-cell detectoris run at approximately 16 MHz with the radiating source running at fullintensity. Since the rotating polygon can rotate at high speeds, anentire 100 mm diameter work piece can be measured in about ten seconds.

In another example, the rotating polygon begins to spin upon power up ofthe device and continues to spin until the entire device is powered off.The constant spinning of the rotating polygon during operation isbeneficial in that spin-up and spin-down delay time is eliminated duringregular operation. The work piece is moved in the direction shown by aprecision stage (not shown) to make a map of the entire work piecesurface. In one embodiment, shown in FIG. 15, the optical inspectorincludes a start of scan photodetector 36 which is placed at the edge ofthe scan line and serves to trigger the acquisition of data samplingwhen the scanned beam passes over the detector 36.

This above process is repeated as the work piece 2 is moved underneaththe optical inspector. A precision stage controller directs the movementof the work piece 34 during the inspection process. In one example, theprocessor 48 outputs defect inspection data which is logged along withthe work piece scan location. The number and location of defects on thework piece will determine the disposition of the work piece. In oneexample, depending upon the location and type of defect, some portionsof the work piece may be useful and others portions of the work piecemay be discarded. In another example, if the work piece has many defectsthen the entire work piece may be discarded.

It is noted herein, that the bi-cell detector 43 is of exemplary use inthis disclosure. One skilled in the art will readily realize that thebi-cell detector 38 may be replaced with various multi-cell detectors toachieve the utility of the present invention.

It is noted herein, that the use of a photomultiplier tube detector 47is of exemplary use in this disclosure. One skilled in the art willreadily realize that the photomultiplier tube detector 47 may bereplaced with other light sensing detectors such as a siliconphotodetector to achieve the utility of the present invention.

FIG. 16 is a top view diagram of a second optical inspector. The opticalinspection illustrated in FIG. 16 performs the same function as theoptical inspector illustrated in FIG. 15, but utilizes additionalmirrors to route the specular reflection and the near specular scatteredradiation along more complex paths.

FIG. 17 is a diagram illustrating a perspective view of a large anglescattered radiation optical inspector.

The optical inspector includes a rotating polygon 91 a telecentric scanlens 92, a stage 100, a blocker 96, a focusing lens 97, an aperture 98,and a detector 101. A radiation source irradiates the rotating polygon91 which directs a moving source beam with varying angular directiononto telecentric scan lens 92. Telecentric scan lens 92 redirects thesource beam with varying angular direction to an angle substantiallynormal to transparent work piece 94. As shown in FIG. 17, the sourcebeam causes a scattered radiation to be radiated from transparent workpiece 94 and stage 100. Scattered radiation from stage 100 occurs due tothe transparency of transparent work piece 94 and transparent platform95. A portion of scanning beam 93 passes through transparent work piece94 and transparent platform 95 and illuminates stage 100. Stage 100 is asurface located below transparent work piece 94. Scattered radiationoriginating from stage 100 is illustrated in FIG. 17. Focusing lens 97,located at an oblique angle from the plane of incidence of the sourcebeam, receives a portion of the scattered radiation originating from thetransparent work piece 94 as shown in FIG. 17. The scattered radiationoriginating from stage 100 passes through transparent work piece 94 andtravels to blocker 96 (not focusing lens 97). Blocker 96 is opaque andeither absorbs or redirects scattered radiation originating from stage100 away from focusing lens 97. As such, only scattered radiation fromtransparent work piece 94 or transparent platform 95 is focused byfocusing lens 97 to focal plane 99. At focal plane 99, aperture 98limits the scattered radiation allowed to pass to large angle scatteredradiation detector 101. In this configuration, the scattered radiationmeasured by scattered radiation detector 101 includes only scatteredradiation from the transparent work piece 94 and the transparentplatform 95. Therefore, blocker 96 allows the measurement of scatteredradiation originating from transparent work piece 94 withoutcontamination of scattered radiation from stage 100.

In one example, blocker 96 is rectangular and opaque like the exemplaryblocker labeled 96A. Blocker 96 is fixed in position with respect to thetelecentric scan lens 92 and does not move during the scanning of thework piece. The scattered radiation originating from the transparentwork piece 94 and transparent platform 95 is not blocked by blocker 96.

Blocker 96 may be implemented in other non-rectangular shapes, such ascircularly shaped blocker 96B, or an epileptically shaped blocker 96C.

The scattered radiation originating from the transparent work piece 94and transparent platform 95 includes scattered radiation from both thetop surface and bottom surface of the transparent work piece 94 andtransparent platform 95. Therefore, the scattered radiation measured byscattered radiation detector 101 includes the scattered radiation fromboth the top surface and bottom surfaces of both transparent work piece94 and transparent platform 95.

FIG. 18 is a diagram of a specular reflection intensity mappingillustrating the specular reflection resulting from the irradiation atposition (X1, Y1) and (X1, Y4) illustrated in FIGS. 2 and 4. Thespecular reflection intensity mapping is generated using measurementsdetected by bi-cell specular reflection detector 43. The measuredspecular reflection intensity measured at location (X1, Y1) is withinthe local average of specular reflection intensity which indicates thatan air gap is not present at location (X1, Y1). Conversely, the measuredspecular reflection intensity measured at location (X1, Y4) is greaterthan the local average specular reflection intensity which indicatesthat an air gap is present at location (X1, Y4).

FIG. 19 is a diagram of a scattered radiation intensity mappingillustrating the scattered radiation resulting from the irradiation atposition (X1, Y2), (X1, Y3), and (X1, Y5) illustrated in FIGS. 6, 7, and9. The scattered radiation intensity mapping is generated usingmeasurements detected by photomultiplier tube 47. The scatteredradiation intensity measured at location (X1, Y2) is greater than thelocal average of scattered radiation intensity which indicates forwardscattered radiation from a top surface particle. The scattered radiationintensity measured at location (X1, Y3) is much greater than the localaverage of scattered radiation which indicates back scattered radiationfrom a top surface particle. The scattered radiation intensity measuredat location (X1, Y5) is much greater than the local average of scatteredradiation which indicates back scattered radiation from a bottom surfaceparticle.

FIG. 20 is a diagram of defect detection and classification logic table.The table includes five columns. One column lists Large Angle ScatteredRadiation (LASR) measurements. The LASR measurement is the differencebetween event peak and a local average of large angle scatteredradiation. One column lists Near Specular Scattered Radiation (NSSR)measurements. The NSSR measurement is the difference between event peakand a local average of NSSR. An example of an event peak and a localaverage is illustrated in FIG. 21. One column is Specular Reflection(SR) intensity measurement. The SR is the difference between event peakand a local average of SR. One column is specular reflection angle (alsoreferred to herein as “surface slope”). Specular reflection angle is thedifference between even peak and a local average of specular reflectionangle. The last column is defect type. Six types of defects are listedin the defect type column.

The first row of the table describes the characteristics of an interfaceparticle defect. When an interface particle is present, the LASR isbelow a measurable threshold or is much less than NSSR measured at thesame location. In one example, measured LASR intensity will be one halfof the NSSR intensity measured at the same location. Conversely, theNSSR will be much great than the LASR intensity measured when aninterface particle is present. The specular reflection will be constant(e.g. no significant change in intensity) or will increase when aninterface particle is present. The specular reflection angle will (i)transition from a positive slope to a negative slope, or (ii) willremain at a constant slope, when an interface particle is present. Whenthe four measurement characteristics listed above are met, the defecttype is determined to be an interface particle as shown in FIG. 1.

The second row of the table describes the characteristics of aninterface bubble. When an interface bubble is present, the LASR is belowa measurable threshold or is much less than NSSR measured at the samelocation. In one example, measured LASR intensity will be one half ofthe NSSR intensity measured at the same location. Conversely, the NSSRwill be much great than the LASR intensity measured when an interfacebubble is present. The specular reflection intensity will be positiveand have a large amplitude when an interface bubble is present. Thespecular reflection angle will oscillate between positive slope andnegative slope across the interface bubble. When the four measurementcharacteristics listed above are met, the defect type is determined tobe an interface bubble as shown in FIG. 1.

The third row of the table describes characteristics of a top surfaceparticle. When a top surface particle is present, the LASR is muchgreater than the NSSR measured at the same location and the LASR shows adouble event where there is another increase in LASR intensity within aclose proximity to the current scan location. In one example, closeproximity is within one hundred micrometers. Conversely, the NSSR willbe much less than the LASR intensity measured when a top surfaceparticle is present. The specular reflection intensity will be close toa local average of specular reflection intensity or will be less thanthe local average of specular reflection intensity. The specularreflection angle will not have any significant change and will remain ata constant angle (e.g. a constant slope). When the four measurementcharacteristics listed above are met, the defect type is determined tobe a top surface particle as shown in FIG. 1.

The fourth row of the table describes characteristics of a bottomsurface particle. When a bottom surface particle is present, the LASR isgreater than NSSR measured at the same location and the LASR shows asingle event where there is not another increase in LASR intensitywithin a close proximity to the current scan location. In one example,close proximity is within one hundred micrometers. Conversely, the NSSRwill be much less than the LASR intensity measured when a bottom surfaceparticle is present. The specular reflection intensity will be close toa local average of specular reflection intensities when a bottom surfaceparticle is present. The specular reflection angle will not have anysignificant change and will remain at a constant angle (e.g. a constantslope). When the four measurement characteristics listed above are met,the defect type is determined to be a bottom surface particle as shownin FIG. 1.

The fifth row of the table describes characteristics of a top surfacepit. When a top surface pit is present, the LASR is below a measurablethreshold or is less than NSSR intensity measured at the same location.Conversely, the NSSR will be greater than the LASR intensity measuredwhen a top surface pit is present. The specular reflection intensitydecreases when a top surface pit is present. The specular reflectionangle either (i) transition from a negative slope to a positive slope,or (ii) remains at a constant angle (e.g. a constant slope) when a topsurface pit is present. When the four measurement characteristics listedabove are met, the defect type is determined to be a top surface pit asshown in FIG. 13.

The sixth row of the table describes the characteristics of a stain.When a stain is present, the LASR is positive and the NSSR intensitymeasured at the same location is less than the LASR intensity. Thespecular reflection intensity decreases when a stain is present. Thespecular reflection angle does not change (e.g. constant slope) when astain is present. When the four measurement characteristics listed aboveare met, the defect type is determined to be a stain.

The algorithm of FIG. 20 may be implemented by software code executed ona processor. Alternatively, the algorithm of FIG. 20 may be implementedby a state machine, lookup table or any other methodologies well knownin the art.

FIG. 22 illustrates a result work piece defect mapping that is generatedby applying the logic described in the table of FIG. 20 to measurementsmeasured across the surface of the work piece. The work piece defectmapping can be used by work piece manufacturers to identify the parts ofthe work piece that are not to have additional processing so as to notwaste resources and further develop a portion of the work piece that isdefective.

FIG. 23 is a flowchart 200 illustrating the steps included in the defectdetection process. In step 201 the work piece is irradiated with ascanning beam. In step 202 large angle scattered radiation is measured.In step 203 near specular scattered radiation is measured. In step 204specular reflection intensity is measured. In step 205 specularreflection angle (surface slope) is measured. In one example, steps 202through 205 are performed contemporaneously. In step 206 the type ofdefect that is present at the scan location is determined using themeasurements taken in steps 202 through 205. In step 206 the type ofdefect determined in step 206 and the scanning location on the workpiece is used to generate a work piece defect mapping.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A method, comprising: (a) directing a scanningbeam to a first location on a first surface of a first transparentsolid, wherein a second surface of the first transparent solid abuts afirst surface of a second transparent solid; (b) at the first location,measuring: (i) specular reflection intensity, (ii) Near SpecularScattered Radiation (NSSR) intensity, (iii) Large Angle ScatteredRadiation (LASR) intensity, and (iv) Specular Reflection Angle, wherein(i) through (iv) result from irradiation by the scanning beam; and (c)storing coordinate values of the first location, and measurements (i)through (iv) in a memory; (d) repeating steps (a) through (c) at aplurality of locations on the first surface of the first transparentsolid; (e) determining if a defect is present at each location; and (f)determining a type of defect when a defect is present, wherein the typeof defect at the first location is an interface particle when: (i) theLASR measured at the first location is less than a first percentage ofthe NSSR measured at the first location; (ii) the specular reflectionintensity measured at the first location is within a second percentageof a local average of specular reflection intensity or greater; and(iii) the specular reflection angle transitions from a positive angle toa negative angle at the first location, wherein the local averages are afunction of a plurality of measurements measured at a plurality oflocations that are within a first distance of the first location.
 2. Themethod of claim 1, wherein steps (a) through (c) are performed withoutthe use of an incoming waveplate, an outgoing quarter waveplate, or apolarizing beam splitter.
 3. The method of claim 1, wherein the firstpercentage is fifty percent, wherein the second percentage is a tenth ofa percent, and wherein the first distance is two hundred microns.
 4. Themethod of claim 1, wherein the type of defect at the first location isan interface bubble when: (i) the LASR measured at the first location isless than a first percentage of the NSSR measured at the first location;(ii) the specular reflection intensity measured at the first location ismore than a second percentage greater than a local average of specularreflection intensity or greater; and (iii) the specular reflection angleoscillates between positive angles and negative angles near the firstlocation, wherein the local averages are a function of a plurality ofmeasurements measured at a plurality of locations that are within afirst distance of the first location.
 5. The method of claim 1, whereinthe type of defect at the first location is a top surface particle when:(i) the LASR measured at the first location is more than a firstpercentage of the LASR measured at the second location, and the LASRmeasured at a first location is more than a second percentage of theNSSR measured at the first location, wherein the first location iswithin a first distance of the second location; (iii) the specularreflection intensity measured at the first location is within a thirdpercentage of a local average of specular reflection intensity, or more;and (iv) the specular reflection angle is within a fourth percentage ofa local average of specular reflection angles, wherein the localaverages are a function of a plurality of measurements measured at aplurality of locations that are within a second distance of the firstlocation.
 6. The method of claim 1, wherein the type of defect at thefirst location is bottom surface particle when: (i) the LASR measured atthe first location is at least a first percentage of the NSSR measuredat the first location; (ii) the specular reflection intensity measuredat the first location is within a second percentage of the local averageof specular reflection intensity; and (iii) the specular reflectionangle is within a third percentage of a local average of specularreflection angles, wherein the local averages are a function of aplurality of measurements measured at a plurality of locations that arewithin a first distance of the first location.
 7. The method of claim 1,wherein the type of defect at the first location is top surface pitwhen: (i) the LASR measured at the first location is within a firstpercentage of a local average of LASR, and less than a second percentageof the NSSR measured at the first location; (ii) the specular reflectionintensity measured at the first location is at least a third percentageless than a local average of specular reflection intensity; and (iii)the specular reflection angle transitions from a negative angle to apositive angle at the first location, wherein the local averages are afunction of a plurality of measurements measured at a plurality oflocations that are within a first distance of the first location.
 8. Themethod of claim 1, wherein the type of defect at the first location is astain when: (i) the LASR measured at the first location is at least afirst percentage greater than a local average of LASR intensities; (ii)the NSSR measured at the first location is less than the LASR intensitymeasured at the first location; (iii) the specular reflection intensitymeasured at the first location is less than a local average of specularreflection intensities; and (iv) the specular reflection angle is withina second percentage of a local average of specular reflection angles,wherein the local averages are a function of a plurality of measurementsmeasured at a plurality of locations that are within a first distance ofthe first location.
 9. The method of claim 1, wherein the firsttransparent solid is one of a group consisting essential of: glass,sapphire, Silicon (Si), and Silicon Carbide (SiC).
 10. The method ofclaim 1, wherein the second transparent solid is one of a groupconsisting essential of: glass, sapphire, Silicon (Si), and SiliconCarbide (SiC).
 11. The method of claim 1, wherein the first and secondtransparent solids are transparent to infrared light.
 12. The method ofclaim 1, wherein the first and second transparent solids are transparentto visible light.
 13. The method of claim 1, wherein one of thetransparent solids is transparent to visible light and the othertransparent solid is transparent to infrared light.